Single-curved vane-type thermally actuated switch



June 14, 1966 E. WOJCIK 3,256,406

SINGLE-CURVED VANE-TYPE 'IHERMALLY AGTUATED SWITCH Filed April 25, 1963INVENTOR.

EDWARD WOJC lK A NEY United States Patent 3,256,406 SINGLE-CURVEDVANE-TYPE THERMALLY ACTUATED SWITCH .Edward Wojcik, Astoria, N.Y.,assignor to Ideal Corporation, a corporation of New York Filed Apr. 25,1963, Ser. No. 275,718 9 Claims. (Cl. 200113) This invention relates tonew and improved switches and elements thereof, particularly of the typeuseful in flasher circuits or for analogous purposes.

One important object of the invention is to provide a snap action switchsuitable for use as a flasher switch or the like, having desiredoperating characteristics which are not substantially affected bynormally occurring variations in the dimensions or properties of thecomponent materials or in the processing and assembly of these materialsto produce the switch, so that the switch may be manufactured reliablyin large quantities by automatic machinery and with minimum need foradjustments by hand.

Another object of the invention is to provide a switch construction foruse in flasher circuits or the like which enables improved control ofthe relative duration of the flash and olf times of the circuits andwill operate advantageously with little or no perceptible differencebetween the duration of the first flash and that of succeeding flashes.

A further object is to provide a snap action switch which may be readilyadjusted to vary its operating characteristics.

Still another object is to provide a snap action switch of the vane typehaving a simple and yet durable construction giving is a relatively longservice life.

The switches provided according to the present invention make use of anelectro-thermally or thermally actuated switching element composed of aresilient vane member of distinctive construction coacting with athermally expansible pull member so as to be constrained to oneswitching position when the pull member is cool and to switch itself toanother position when the pull member is suitably heated, as by thepassage of an electrical current through it to heat it by electricalresistance.

The vane member comprises a body leaf of suitably thin and resilientsheet metal or the like, which by being suitably pre-stressed or formedto a naturally curved shape is intrinsically biased toward a naturalposture in which it is bowed relative to one axis only into a curvature,preferably having substantially the form of a minor sector of acylinder, that protrudes to one side of a plane intersection oppositeend portions of the leaf. Instead of being allowed to hold this naturalposture, the resilient leaf has the thermally expansible pull member sotensioned over its naturally convex side that the pull member normallyconstrains it, against its intrinsic bias, into an inverted posture inwhich it is bowed elastically relative to one axis only into a curveprotruding to the other side of a plane intersecting said end portions.

The intrinsic bias of the leaf and the expansibility of the pull memberare selected so that upon a heating of the pull member to relax itstension, such as by passing an electrical current through it, the pullmember no longer can constrain the inversely bowed leaf to its invertedposture; so the leaf then inverts itself toward its natural posture.

The motion attending each inversion of the leaf is readily utilized toeffect a switching action. Through electrical heating of the pullmember, the switching element can be caused to switch quickly from anormal or cool position to a second position in which the leaf hasassumed or approached its natural posture. When the leaf approaches thatposture the pull member lies flush against the naturally convex side ofthe leaf; so the pull member is then cooled and contracted quickly byconduction of heat into the relatively cool body of the leaf. In thisway the leaf is returned quickly to its inverted posture for thecompletion of a switching cycle that can 'be repeated reliably timeafter time over prolonged periods of time.

According to another important feature of the invention, the inversionsof the bowed leaf and the attendant switching motions are caused to takeplace in each instance with an advantageous snap or toggling action, byproviding the vane member with suitable means acting on the oppositeends of the leaf to resist spreading of the leaf so that it must buckleor toggle upon being inverted across the plane intersecting its ends.For this purpose, the vane member may be formed with a side stripjoining the ends of the bowed leaf in chordal relation to the leaf at alocation adjacent to at least one of its side edges. The strip can beformed out of the same piece of sheet metal as the leaf.

The action of the switching element can be easily modified or controlledby making the side strip or strips stretchable under a certain tensionapplied thereto by the leaf so that a certain desired resistance will beimposed to each inversion of the leaf.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following detailed description of apreferred embodiment there of and from the accompanying illustrativedrawing in which:

FIGS. -1 and 2 are isometric views taken from opposite sides of a snapaction switch embodying the invention;

FIG. 3 is a schematic edge view of the vane member employed in theswitch of FIGS. 1 and 2; and

FIGS. 4-7 are schematic views illustrating successive stages in thesnapping movement of the switching element between contact open andcontact closed positions.

Referring to the drawing, the basic switching element of the switchshown includes a vane member 10 made from a generally rectangular pieceof relatively stiff thin sheet metal such, for example, as spring steelin sheet or strip form of about .005 inch thickness. The piece isslotted along one side edge thereof to provide therealong a side strip16 separated from a relatively wide body leaf 14 by a slot 12, with theside strip joined integrally at its ends to opposite end portions 15 and17 of the leaf.

The body leaf 14 is permanently stressed or set to a substantiallycylindrically curved natural posture toward which it is always biased byits intrinsic resiliency. In that posture it is bowed relative to oneaxis only into a curve protruding to one side of a plane intersectingthe end portions 15 and 17, for example, to one side of the planeoccupied by strip 16 as indicated schematically in FIG. 3. The sidestrip 16 is crimped as indicated at 18, so that its normal lengthcorresponds substantially to that of a chord joining the ends of thebowed leaf 14.

Thus, when the vane member is in its natural or unconstrained conditionindicated in FIG. 3, it resembles an archery bow having a relativelythin and wide bowed body with the bowstring disposed at one edge of thebody, but with the body holding itself bowed instead of being bowed bytension in the string, or side strip 16. The side strip resistsspreading of the end-portions 15 and 17 where it joins them together butdoes not prevent inversion of the curvature of the body leaf 14.

The basic switching element includes also an expansible pull member 20that is trained over and governs the postures of the vane member 10. Thepull member preferably is a thin narrow band or wire of an electricalresistance alloy, such, for example, as a flat chromiumnickel alloy wireof the type known as Nichrome, havcurvature inverse to the pre-setnatural bowing or curvature thereof.

The pull member 20 normally lies substantially in a chordal planeinterconnecting the end portions and 17 of the inversely bowed leaf,thus extending over the side 14B thereof substantially as illustrated inFIG. 4 and acting, much as the string of an archery bow, to hold theleaf bowed elastically in the direction opposite to the natural orpre-set bowing thereof, against the intrinsic bias thereof.

The length and the electrical resistance and thermal expansionproperties of the pull member are readily selected so that when thetemperature of this member is increased, as by the passage of anelectrical current through it, the pull member Will expand to relax itstension and the bending moment which it exerts upon the ends of the bodyleaf. The pull member then will no longer overpower the intrinsic biasor shape restoring force of the body leaf, whereupon the latter invertsitself and returns to its own natural or preferred posture.

As the pull member becomes relaxed the intrinsic bias of the body leafapplies an increasing tension to the side strip 16, which strip byresisting this tension resists spreading of the end portions 15 and 17and flattening of the leaf 14 in the course of the return of the latterto its normal posture. The return movement of the leaf therefore isaccompanied by a buckling of its thin body, which begins on one side ofthe plane of the tension of strip 16, as illustrated schematically inFIG. 5, and which upon progressing sufliciently to the other side ofthat plane causes the leaf to snap with a toggling action to its naturalposture, whereby the switching element shown is moved to its preferredposition illustrated schematically in FIG. 6.

A similar buckling and toggling action in reverse direction, asillustrated schematically in FIG. 7, occurs upon a contraction of thelength of the pull member 20, such as that brought about by a cooling ofit from the elevated temperature at which it allowed the body leaf toassume its natural posture. curvature of the leaf is inverted, againwith a snap action, and the switching element takes the position towhich it is biased by the pull member 20, as illustrated schematicallyin FIG. 4.

The vane member 16 and pull member 20 constitute an effective snapaction switching element suitable for many uses. It is particularlysuitable for use as the working element of an improved flasher switchsuch as that shown in FIGS. 1 and 2.

As there shown, the flasher switch includes a circular frame or base 26of electrical insulating material, to which are secured a prong orterminal 28 and also, as by a rivet 29, a bracket 30 having one end bentdownwardly and passed through the base 26 to form a second prong orterminal 32. The other end 34 of bracket 30 is enlarged and supports amounting element 38. This mounting element is electrically insulatedfrom the bracket, as by suitable dielectric sheet material 36, and isformed with an upstanding arm 40.

The switching element is mounted on the free end of the upstanding arm40, as by a rivet or a spot weld at 42 which fixes the body leaf 14 tothe arm at a point disposed toward One end of the leaf 14, considerablyto one side of the apex or center of the pre-set curvature thereof.

An electrical contact element 48 is fixed to the leaf 14 at a locationthereon disposed away from the mounting point 42, advantageously towardthe other end of the In this way the bowing or l leaf at a considerabledistance to the other side of the apex or center of said curvature. Thecontact element 48 coacts with a mating contact element 46 which ismounted on the free end of a finger 44 struck upwardly from one side ofthe bracket 30. The finger 44 so positions contact element 46 that whenthe pull member 20 is in its normal or cold condition, the body leaf 14then being held in its reversely bent or inverted posture, the twocontact elements 46 and 48 are pressed firmly together in circuitclosing relation to form a closed path for conducting electrical currentbetween the terminals 28 and 32 through the thermally expansible pullmember 20.

The contact elements then connect the vane member 10 with bracket 30,thus with terminal 32. The vane member is at all times connectedelectrically with terminal 28 through the expansible pull member 20, asby a conductor 50 of low electrical resistance which is secured at oneend, as by welding, to substantially the midpoint of the pull member 20and is secured at its other end, as by welding, to a finger 28a on theupper end of the prong or terminal 28.

Instead of securing the conductor 50 to the pull member by welding, oneend of the conductor may be secured to a tab formed integral with thepull member; or a conductor formed as one piece with the pull member maybe provided to connect member 26 with terminal 28.

It will be evident that when the switch is in the position indicated inFIG. 1 and the terminals 28 and 32 are connected into an electricalcircuit, electrical current will flow between the terminals by passingthrough the high resistance pull member'Zt). The pull member then heatsand expands until it no longer restrains the leaf 14 to the invertedcircuit closing posture illustrated in FIGS. 1 and 4. Thet leaf thenbegins to buckle or unbend, as illustrated in FIG. 5, toward its ownnatural or preferred posture, under its own bias which it exertscontinuously while it is bent elastically out of that pre-set posture.In the course of this buckling or unbending action, the leaf snaps toits natural posture and thus snaps the switching element to its hot orcircuit opening position illustrated in FIG. 6, through a rocking ordeflection of the switching element about its mounting point 42 wherebythe portion of the 'body leaf carrying contact element 48 is moved awayfrom contact element 46 to break the circuit through the switch.

When the switch reaches its hot or open position, the contact carryingside 1413 of leaf 14, although having been held concave by the pullmember while that member is cool, is inverted to its intrinsicallyconvex curvature;

.if desired a lesser length of the pull member may be caused to contactthe leaf surface, as by forming the end portions 15 and 17 with raisedcorner portions over which the pull member will extend from its fixedends 22 and 24.

Since the leaf is highly heat conductive, relatively massive and coldcompared to the expanded pull member, the heat of the pull member lyingin contact with side 14B is quickly drawn away by conduction through theleaf. Thus the pull member is quickly cooled and contracted, and as itcontracts it buckles the leaf against the pre-set bowing thereof so asto move it back to its inverted, circuit closing posture of FIGS. 1 and4. A probable condition in the course of this invention is indicated inFIG. 7.

When the contact elements 48 and 46 again come together, theyreestablish the circuit through the pull member, and the cycle isrepeated. The switch thus continues to open and close the circuit atregular intervals for as long as the actuating electrical circuit intowhich it is connected is maintained.

The described coaction of the hot pull member and the relatively coldleaf provides important advantages in the use of the switch. The timerequired for the cooling or open circuit stage of the switch operationcan be made shorter than would otherwise be the case. Moreover, thelength of this interval can be selected and kept in any of variousdesired relationships to the time provided for the flashing or closedcircuit stage of the operation. In other words, various desiredcombinations of flash and off times can be provided. Further, the switchwill operate in the first of its cycles with very nearly the same flashand off times as in succeeding cycles, which contributes to theeffectiveness of its use as a flasher switch for the control of warningsignals of atuomobiles or other vehicles.

Since the leaf of the vane member is devoid of vpre-set crimps or bossesand undergoes its inverting move- The crimping of the side strip 16, inaddition to shortening it to approximately the chordal length of thebowed body leaf, gives the side strip longitudinal stretchability andthe effect of a tension spring imposing, a certain resistance to theinversions of the curvature of the leaf. The magnitude of thisresistance can be set at any of a variety of desirable values by controlof the stretch resistance of the crimped side strip. In this way theoperating characteristics of the switch can be readily fixed andcontrolled, as desired in manufacturing practice, without beingsubstantially altered by minor variations commonly encountered in thedimensions or properties of the materials used for the manufacture ofthe switch or in the precision of assembly of its parts. The switch,therefore, can be manufactured to high performance standards with theuse of automatic machinery.

Moreover, the crirnped construction of the side strip 16 provides aconvenient and easy means of adjusting the operating characteristics ofa given switch. When a switch made according to the invention is foundto operate otherwise than in accordance with prescribed specifications,it may be made to meet such specifications by an alteration of thecrimping of the side strip.

Since the leaf 14 is uniformly curved and undergoes its inversionmovements over substantially its entire length, the mounting point42'and the contact element 48 may be located at any of a variety ofpoints over its area, provided only that they are spaced apartlongitudinally of the vane member so as to give the required separatingmovement of the two contact elements. The extent of{ this movement canbe selected as desired by selection of the longitudinal spacing of point42 and element 48 on the leaf 14.. The pressure of element 48 againstelement 46 in the closed position of the switch and the motion ofelement 48 relative to element 46 as these elements make and breakcontact, can each be similarly selected and controlled.

It has been found, for example, that by locating the mounting point 42and element 48 toward opposite ends of the leaf, substantially asillustrated, several desirable attributes are attained. Contact element48 undergoes an advantageous rocking movement while engaging ordisengaging element 46, whereby pitting or fusing of the contactelements is avoided or inhibited. The contact elements are heldtogether, when engaged, under a pressure sutficient to assure a largearea of mutual contact and a low resistanceto the flow of currentthrough them. And when the elements are disengaged they are spaced apartfar enough to prevent bridging of the gapby fused material that commonlytends to build up on the face of one of the contact elements in thecourse of long service of the switch.

The snap action switch of the invention will thus be seen to providemany distinct advantages in ease and cost of production and inefficiency and durability of operation.

Although an illustrative embodiment of the invention has been describedin detail herein with reference to the accompanying drawing, it is to beunderstood that the invention is not limited to the illustratedembodiment and that various changes and modifications may be effectedtherein without departing from the scope or spirit of the invention.

What is claimed is:

1. A switching element including a vane member comprising a resilientleaf intrinsically biased over substantially its entire area betweenopposite end portions of the leaf toward a natural posture in which itis bowed in a single-curved form only to one side of a planeintersecting said opposite end portions, and

a thermally expansible pull member tensioned between said end portionsover the naturally convex side of said leaf and normally constrainingsaid leaf against its intrinsic bias into an inverted posture in whichit is bowed elastically to the other side of said plane in asingle-curved form only from one to the other of said end portions,

the intrinsic bias of saidleaf and the expansibility of said pull memberbeing sufficient that upon a heating of said pull member to relax itstension said leaf will invert itself toward said natural posture.

2. A switching element including a vane member comprising a resilientleaf intrinsically biased over substantially its entire area betweenopposite end portions of the leaf toward a natural posture in which itis bowed in a single-curved form only to one side of a planeintersecting said opposite end portions, and

a thermally expansible pull member tensioned between said end portionsover the naturally convex side of said leaf and normally constrainingsaid leaf against its intrinsic bias into an inverted posture in whichit is bowed elastically to the other side of said plane in asingle-curved form only from'one to the other of said end portions,

the intrinsic bias of said leaf and the expansibility of said pullmember being sufficient that upon a heating of said pull member to relaxits tension said leaf will invert itself toward said natural posture,

said pull member lying flush against said naturally convex side when theleaf reaches its natural posture, whereby the pull member is then cooledand contracted quickly by conduction of heat into the leaf so as toreturn the leaf quickly to its inverted posture.

3. A switching element including a vane member comprising a resilientleaf intrinsically biased over substantially its entire area betweenopposite end portions of the leaf toward a natural posture in which itis bowed in a single-curved form only to one side of a planeintersecting said opposite end portions, and

a thermally expansible pull member tensioned between said end portionsover the naturally convex side of said leaf and normally constrainingsaid leaf against its intrinsic bias into an inverted posture in whichit is bowed elastically to the other side of said plane Y in asingle-curved form only from one to the other of said end portions,

the intrinsic bias of said leaf and the expansibility of said pullmember being sufiicient that upon a heating of said pull member to relaxits tension said leaf will invert itself toward said natural posture,

said pull member comprising a wire stretched diagonally over said leafbetween diagonally opposite corners of the leaf.

4. A switching element including (a) a vane member comprising (1) aresilient leaf intrinsically biased over substantially its entire areabetween opposite end portions of the leaf toward a natural posture inwhich it is bowed in a single-curved form only to one side of a planeintersecting said opposite end portions, and (2) strip means extendingbetween said end portions in chordal relation to said bowed lea-fadjacent to at least one side edge thereof to resist spreading of theleaf so that the leaf will buckle upon being inverted across said plane,and (b) a thermally expansible pull member tensioned between said endportions over the naturally convex side of said leaf and normallyconstraining said leaf against its intrinsic bias into an invertedposture in which it is bowed elastically to the other side of said planein a single-curved form only from one to the other of said end portions,

the'intrinsic bias of said leaf and the expansibility of said pullmember being sufficient that upon a heating of said pull member to relaxits tensionsaid leaf will invert itself by toggle action and therebysnap toward said natural posture.

5. A switching element according to claim 4, said strip means beingstretchable by the tension applied thereto by said leaf as said pullmember expands, whereby the in version of the leaf is controlled by thestretch resistance of said strip means.

6. A switching element including a vane member in the form of a unitarypiece of uniformly thin resilient sheet metal slotted along a side edgethereof to provide therealong a side strip joining opposite end portionsof a relatively wide body leaf formed by the remainder of said piece,

said leaf having from end to end thereof an intrinsic substantiallyuniform curvature biasing it toward a natural posture in which it isbowed between its ends in a single-curved form only protruding to oneside of said side strip, said side strip being crimped to shorten it andrender it stretchable elastically by the intrinsic bias of the bowedleaf, and a thermally expansible electrical resistance wire tensionedover the naturally convex side of said leaf between opposite endportions thereof and normally constraining said leaf against said biasinto an in- Y verted posture in which it is bowed elastically in asingle-curved form only protruding to the opposite side of said strip,

said bias and the expansibility of said wire being sufficient that upona heating of said wire by passage of an electric current through it saidleaf will invert itself and snap toward said natural posture. 7. Aswitching element according to claim 6, said wire being flat and lyingin face to face contact with said naturally convex side when said leafapproaches said natural posture, whereby the Wire is then cooled andcontracted quickly byconduction o-f heat into the leaf so as to returnthe leaf quickly to said inverted posture.

8. A snap action switch comprising a switching element as defined inclaim 6,

a base,

first and second terminals, a first contact element and a mountingelement, all carried by said base,

said first contact element being electrically connected to said firstterminal and said mounting element being electrically insulated fromsaid terminals,

said switching element being fixed to said mounting element at a pointon said leaf toward one end of said left whereby said switching elementis movable angularly relative to said mounting element by inversion ofthe bowing of said leaf,

said leaf carrying at a point toward the other end thereof a secondcontact element bearing against said first contact element when saidleaf is in said inverted posture,

and means electrically connecting said resistance wire to said secondterminal so that when a circuit is closed to said terminals current willflow through said wire to heat and expand it and thereby cause saidswitching element to break circuit by inversion of said lea-f away fromsaid first contact element.

9. A switching device comprising a resilient vane of electricallyconductive material,

a thermally expansible electrical resistance member tensioned betweenopposite portions of said vane and normally holding said vane bowed toone posture,

the material of the said vane being itself biased so that said vane willdeflect toanother posture upon an expansion of said resistance member,

a mounting member having a body portion of said vane fixed thereto,

a first electrical contact element on another body portion of said vane,

a complementary electrical contact element fixed relative to saidmounting member in position to be engaged by said first element whensaid vane is in said one posture,

said contact elements being disengaged by deflection of Said vane tosaid other posture,

and a flexible electrical conductor fixed to said resistance member forconducting thereto current to heat and expand the same.

References Cited by the Examiner UNITED STATES PATENTS 7 2,363,28011/1944 Arnold 200-113 2,537,485 1/1951 Stizer et al. 200-137 2,574,86911/1951 Green 200-67 2,700,083 1/1955 Harmon 200-113 1 2,712,045 6/1955Welsh 200-122 2,834,853 5/1958 Hood 200-138 2,861,149 11/1958 Hollis etal. 200-113 2,870,292 1/1959 Welsh 200-113 2,878,340 3/1959 Uhl 200-1133,057,982 10/1962 Grover et al 200-138 3,080,464 3/ 1963 Kurz 200--1223,098,139 7/1963 Bleiweiss et al. 200-137 BERNARD A. GILHEANY, PrimaryExaminer. LAURENCE A. WRIGHT, Assistant Examiner.

1. A SWITCHING ELEMENT INCLUDING A VANE MEMBER COMPRISING A RESILIENTLEAF INTRINSICALLY BIASED OVER SUBSTANTIALY ITS ENTIRE AREA BETWEENOPPOSITE END PORTIONS OF THE LEAF TOWARD A NATURAL POSTURE IN WHICH ITIS BOWED IN A SINGLE-CURVED FORM ONLY TO ONE SIDE OF A PLANEINTERSECTING SAID OPPOSITE END PORTIONS, SAID A THERMALLY EXPANSIBLEPULL MEMBER TENSIONED BETWEEN SAID END PORTIONS OVER THE NATURALLYCONVEX SIDE OF SAID LEAF AND NORMALLY CONSTRAINING SAID LEAF AGAINST